The 20-year-old becomes Martin Ling's first signing since taking charge of the Robins earlier this month.
Calvin was released by Oxford in April 2014 and has since spent time with non-League duo Daventry and Hampton & Richmond Borough.
Swindon have now moved to recruit the youngster on a short-team deal, with the League One outfit hovering just one place above the drop zone.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Gillingham | 9 | 6 | 1 | 2 | 12 | 3 | 9 | 19 |
| 2 | Notts County | 9 | 5 | 3 | 1 | 17 | 8 | 9 | 18 |
| 3 | Walsall | 9 | 6 | 0 | 3 | 17 | 10 | 7 | 18 |
| 4 | BarrowBarrow | 9 | 5 | 1 | 3 | 11 | 6 | 5 | 16 |
| 5 | Doncaster RoversDoncaster | 9 | 5 | 1 | 3 | 12 | 12 | 0 | 16 |
| 6 | Fleetwood TownFleetwood | 8 | 4 | 3 | 1 | 16 | 9 | 7 | 15 |
| 7 | Port Vale | 9 | 4 | 3 | 2 | 14 | 12 | 2 | 15 |
| 8 | Grimsby Town | 9 | 5 | 0 | 4 | 13 | 14 | -1 | 15 |
| 9 | Newport CountyNewport | 9 | 5 | 0 | 4 | 15 | 17 | -2 | 15 |
| 10 | Chesterfield | 9 | 3 | 4 | 2 | 15 | 8 | 7 | 13 |
| 11 | AFC Wimbledon | 6 | 4 | 1 | 1 | 9 | 4 | 5 | 13 |
| 12 | Crewe AlexandraCrewe | 8 | 4 | 1 | 3 | 8 | 9 | -1 | 13 |
| 13 | Bradford CityBradford | 9 | 3 | 3 | 3 | 11 | 10 | 1 | 12 |
| 14 | MK Dons | 9 | 3 | 2 | 4 | 12 | 11 | 1 | 11 |
| 15 | Colchester UnitedColchester | 9 | 2 | 4 | 3 | 13 | 15 | -2 | 10 |
| 16 | Cheltenham TownCheltenham | 9 | 3 | 1 | 5 | 11 | 14 | -3 | 10 |
| 17 | Tranmere RoversTranmere | 8 | 2 | 4 | 2 | 4 | 8 | -4 | 10 |
| 18 | Harrogate TownHarrogate | 9 | 3 | 1 | 5 | 9 | 16 | -7 | 10 |
| 19 | Bromley | 9 | 2 | 3 | 4 | 12 | 14 | -2 | 9 |
| 20 | Salford City | 8 | 2 | 3 | 3 | 5 | 9 | -4 | 9 |
| 21 | Swindon TownSwindon | 9 | 1 | 4 | 4 | 9 | 13 | -4 | 7 |
| 22 | Carlisle UnitedCarlisle | 9 | 2 | 0 | 7 | 10 | 19 | -9 | 6 |
| 23 | Morecambe | 9 | 0 | 4 | 5 | 7 | 12 | -5 | 4 |
| 24 | Accrington StanleyAccrington | 8 | 0 | 3 | 5 | 9 | 18 | -9 | 3 |
| > League Two Full Table | |||||||||
